iCal server corrupts clients calendars

Hi,

I have searched the internet flat and cannot seem to find a reason for this. I set up Leopard server and updated to 10.5.6. If I set up the iCal server, then open anyones iCal that is attached, their iCal loses all its calendars. i.e. the list of calendars on the left is missing. If I try add a calendar it lets me but still doesn't show up. No appointments show up either.

I get the following error in my system.log:
May 20 16:31:29 macserver iCal[268]: * -[NSURL initWithString:relativeToURL:]: nil string parameter
May 20 16:31:29 macserver iCal[268]: Exception in -[CalDAVAccountRefreshQueueableOperation refreshWithExceptionHandling] :: * -[NSURL initWithString:relativeToURL:]: nil string parameter
May 20 16:31:51 macserver servermgrd[62]: servermgr_calendar: created default calendar virtual host
May 20 16:32:16 macserver iCal[284]: * -[NSURL initWithString:relativeToURL:]: nil string parameter
May 20 16:32:16 macserver iCal[284]: Exception in -[CalDAVAccountRefreshQueueableOperation refreshWithExceptionHandling] :: * -[NSURL initWithString:relativeToURL:]: nil string parameter

I had copied the files in my Calendars folder to a backup. I shut down the server, then went to my iMac and deleted all my calendars and plists relating to iCal. I rebooted, put the backup files back, opened iCal and it all works again. But put the server on, and everything is lost again.

Any ideas?
I then restarted